2013 BMW M550d xDrive

The ultimate compression-ignition machine?

Lately, BMW has been stretching its M division’s portfolio further than anyone would have expected a few years ago. Widespread automatic transmissions? Sure, who wants to mess with a manual anymore? Turbocharging? Everywhere, please, and we’ll bill it as “Efficient Dynamics.” And an M-powered SUV? Just what the customer wants, so let’s make two. Of all things, however, perhaps a diesel-driven M is a stretch too far. Thus, to occupy the space between the M division’s broadened portfolio and the regular BMW lineup, the M Performance line was created, with the M550d xDrive as its poster boy. We spent two weeks with the car on its German home turf.

In what has become an unfortunate hallmark of nearly every manufacturer, the 550’s model designation does not even remotely hint at its actual displacement. There is no 5.0-liter V-8 under its hood; in fact, BMW has left the V-8 diesels to Audi and Volkswagen altogether. Power comes from the well-proven 3.0-liter straight-six, here producing 376 hp, available between 4000 and 4400 rpm. Maximum torque is 546 lb-ft, served up between 2000 and 3000 rpm. Those are mouthwatering figures, regardless of what kind of fuel the engine is drinking.

To make sure this high-performance diesel doesn’t ever run out of breath, BMW has fitted it with three BorgWarner-supplied turbochargers. Yes, three. Here’s how it all works: At low rpm, a small turbocharger provides initial boost and ensures quick launches. Around 1500 rpm, a large turbocharger takes over, allowing the engine to reach its maximum torque. From 2700 rpm onward, a small, third turbo compresses the air before it reaches the large turbo. Maximum pressure for the system is 50.8 psi.

BMW says the engine was strengthened for this extra dose of power and torque that is made possible in part by an injection system that squirts fuel at 31,900 psi. (For comparison, the twin-turbo 535d’s operates at 26,100 psi.) On the M550d sedan and wagon, power is fed to all four wheels through a ZF-sourced eight-speed torque-converter automatic and BMW’s all-wheel-drive system. All this technology comes with a weight penalty, and in this case, the curb weight is about 4350 pounds.

But the chassis handles this car’s excessive weight remarkably well. The M550d remains neutral up to the limit, and there is virtually no body roll. As with the rear-drive M5 and all other xDrive 5ers, the M550d comes with hydraulic power steering, and it’s better than the soulless electromechanical setup that plagues its less powerful rear-wheel-drive siblings. Still, it’s remote and fails to live up to the BMW ideal. The car we drove was fitted with standard 245/40 rubber up front and 275/35 in the rear on 19-inch wheels; 20-inch wheels are optional.

As the power output suggests, performance is good. We estimate a 0-to-60-mph trip taking just under five seconds. No one’s complaining about that kind of straight-line talent, especially since it is accompanied by a pleasant—if artificially enhanced—snarl. The M550d really shines at triple-digit speeds, which is where you feel its extra muscle and where you realize this diesel’s atypical willingness to rev. Even accelerating from 120 and higher mph is a quick and effortless affair, making the tri-turbo perfect for long autobahn drives. Its mileage, however, is not spectacular for a diesel: The 37-mpg score in the optimistic European cycle contrasts with real-life consumption that hovers in the 20s. And dynamically, the M550d doesn’t even remotely come close to an M5. Throttle response is still diesel-like, which is to say slightly delayed. It feels more like a glorified 535d, not an M, so perhaps there was some wisdom in creating the M Performance line after all.

This impression is confirmed by the available electronic settings. The M550d doesn’t let you play with important parameters—steering, throttle, transmission, stability control—separately as you can in the M5. Instead, you have to choose between prepackaged driving modes that include an annoyingly sluggish eco pro mode. Sport plus, at the other end of the spectrum, was our favorite, being the only way to get adequate response from the right pedal and activate the exhaust noisemaker. But it’s far from perfect; the shift schedule keeps the diesel at unnecessarily high revs, and the transmission refuses to move into top gear. Shifting the futuristic gear selector back and forth between “D” and “S” doesn’t change anything, so we ended up fiddling with the manual mode. When in sport plus, an annoying warning light informs you that the stability-control system is not fully operative, but it’s kind of a lie, since the car will only allow some slight drift angles before reining you in and reactivating the system. And when ESP reengages, the more aggressive throttle response and the extra sound go out the window.

Although the M550d doesn’t look that different from a standard-issue 5-series, it actually does have some M Performance–specific bits. There is a horizontal blade in the lower front fascia, and the mirrors are painted gray. Rectangular exhaust tips are taken from the 550i’s parts bin. The steering wheel and the footrest are graced by M logos. But the aero kit is virtually identical to the M Sport package that you can get with any engine, while sharing no parts with the actual M5.

This ultimate oil burner won’t be offered in the U.S., which is not a terrible loss. The M550d xDrive makes sense if you plan to cover long distances at triple-digit speeds but have no desire to fill up every 250 miles, as required by an M5. For any other application, the single-turbo 530d or the twin-turbo 535d would be just about perfect—and depending on the market, you can get them without all-wheel drive as well, shaving some of this sedan’s excessive weight.

In Germany, the M550d xDrive retails at the eye-watering equivalent of about $80,300 before taxes. That’s a good $24,000 on top of the price of a European 535d xDrive. This hike is a bit hard to justify, even given the great pile of technology underhood and the accompanying M badging. Even as an “almost” M car, we think this top-of-the-line diesel might be too far of a stretch for BMW.

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